Drive mechanism



Aug. 4, 1953 M. BARKER 2,647,752

DRIVE MECHANISM Fiied Aug. 23, 1950 Ffgz lfiventoh Leonard M.Bar-Ker-,

byZZyZZZILJ His Attorney.

Patented Aug. 4, 1 953 DRIVE MECHANISM Leonard M. Barker, North Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application August 23, 1950, Serial No. 180,973 A 2 Claims. (Cl. 27420) This invention relates to drive mechanisms particularly applicable to transducing systems.

Recording and reproducing equipment usually comprises a transducing head whichis brought into signal transfer relationship with a recording material. Where the intelligence is stored, or is to be stored in a plurality of tracks on the surface of the record material, means must be provided for driving the transducing head to scan therecording material surface. A special need exists in the case of repetitive, short-time transducing operations for a simple, inexpensive and reliable drive mechanism. Also, a drive mechanism which permits readily, minor adjustments of tracking motion and start-stop action of a transducing cycle is of special importance where rapid message changes are to be accommodated.

It is an object of my invention to provide novel means for imparting an axial shaft motion.

Another object of my inventionis to provide novel means for imparting axial and rotational shaft motion.

' Another object of my invention is to provide a novel drive mechanism and control for use in recording systems.

Another object of my invention is to provide a simple and inexpensive drive and'con'trol mechanism for effecting recording or playback of intelligence. In accordance with an embodiment of my invention applicable to magnetic playback systems, a drive shaft carryinga pickup head at one end is mounted coaxially with a drive gear and arranged to rotate relative to the gear about its axis. A helical cam carried by the gear engages a mating cam or member carried by the shaft to cause axial displacement of the shaft relative to the gear when the gear turns, thereby causing the pickup head to scan a recording material surface. Friction forces developed between the helical cam and mating member during rotation of the helical cam provide contact pressure of the pickup head on the recording material. In addition, axial movement of the drive shaft is caused to operate a switch controlling drive gear operation.

The novel features which I believe characteristic of my invention are set forth with particularity in the appended claims. My invention, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference tothe following description taken in connection with the accompanying drawing, wherein Fig. 1 illustrates in part-section the na- 2 ture of the drive mechanism and Fig. 2 illustrates schematically a detail of the arrangement of Fig. 1.

Referring to Fig. 1, there is disclosed a magnetic reproducing system for repeating messages of short duration whenever a switch is tripped. The switch may be tripped by a person opening a door, stepping on a mat, interrupting a light beam, dropping a coin in a vending machine, by the operation of a timing cam or other means. When the switch is tripped by some external means, not shown in the drawing, motor I is energized and drives an output shaft 2 by means of a helical gear 3. Attached to the output shaft 2 is a cylindrical drum 4 holding alengt-h of magnetic material 5, such as a'magnetic tape wrapped or deposited along its peripheral surfaces. A

pickup head 6 rides on the tape and is'givenlata eral motion by means of a cam arrangement, to" be disclosed shortly, so as to traverse a helical track on the tape. In scanning the intelligence stored magnetically in the tape or record material'5, a small voltage is developedin the pickup head, amplified and applied to a speaker, not shown. When the pickup head 6 has moved sufiiciently in a lateral direction, the shaft I to which itis attached opens a set of contactsS and 9 to stop the motor I. By closing external switch 10 for a short time, the motor is reenergized to initiate a new cycle.

Referring to Fig. l in detail, motor! is caused to operate by supplying an alternating voltage over lead H directly to one terminal of the motor and over lead [2 through the normally closed switch contacts fl'and 9 to the other terminal of the motor. The motor I operates to drive helical gear'3 which causes output shaft 2 to rotate in the direction shown by arrow [3. Output shaft 2 passes through a bearing I4 carried inthe housing l5 for supporting the drum 4 carrying the recording material 5 along its peripheral surface. The other end of the output shaft is supported in the bearing I6 press fitted in housing [5. A'wing nut I1 engages the threaded end portion at output shaft 2 for rigidly forcing the drum 4, slipped over the output shaft, against the collar I8 secured to shaft 2. In a preferred embodiment, collar l8 has a protrusion which engages drum 4 to provide proper indexing of drum 3.

Idler gear l9, carried by shaft 20 mounted on housing I5, is driven by pinion gear 2| carried by shaft 2. In turn, idler gear I 9' drives the camgear'22 carriedby the drive shaft 1. Thus, idler gear l9 imparts motion from gear 2| splined on shaft 2 to cam gear 22, which is constrained displaceable with respect to the cam gear. The

cam gear 22, which is free to rotate on its shaft 1, has a 360 helical cam 26 cut on the end sur-' faces of its boss for engaging a mating camor member linked to the drive1'shaft 1 byzmeans' of set screw 287 Since shaft 1 is prevented from rotating because of contact of pickup .head 6 with drum 4, the two cams will'mov'e axially with respect to each other in accordance with the angular rotation of the cam gear 22. Upon completion of one revolutionof shaft l, the two cams26= and 2'! snap together to return the shaft axially to its original position. Although the preferred embodimentshown in Fig-1 employs a -'helical' driving andmating cam- 26 and 2'1, respectively,gone of the cams, for example 21, maybe replaced with a stop, such as a pin protruding radially from. the shaft i. The radial and lateral motionf shaft 1 is still obtainable with this latter arrangement.

Rotation of-the cam gear' 22, riding against thebearing '23 in the housing [5, drives the mating'cam2l axially, thereby imparting lateral motion' to the pickup head by means of drive shaft 1. To insure proper contact between the cams, and :thereby insure proper lateral motion ofthe pickup head, the cams are spring loaded. Coil spring 29, mounted coaxiallywith the drive shaft 1,"is=mounted at one end on a shoulder 36- carried'by mating cam 21 to keep the spring from interfering with the motion of shaft 1. Asimilar shoulder 3 l-= is provided on the bearing 25;

As'sthe cam gear' I 26' approaches the completion of one'revolution, the mating cam or member'21 is arranged to push-the shaft '1 to which it is fastened axially against fiber piece 32' carried'bYIcontact arm-'33.- As the contact arm 33-"moves,"contact 9, supported by'31-l, breaks with contact 8, thereby'openin'g themotor'energizing lead 12 and halting motor operation; Both contact arms 33' and 34'spa'cedby insulating washers 35' are mounted by means of a nut and bolt assembly 3B tospring leaf '3'!" supported by the switch bracket 25; The'point at which the conta'cts 8 and 9 open may be adjusted-by-turning machine screw '38, threaded in the bracket 25. Thus;: driving the machine screw towards-the leftcause's the contacts to open earlier in the cycle,-'whereas driving the machine screw to the right causes the contacts toopen later in the cycle! Thus,: besides providing a simple and reliable scanning motion for the transducin'g head 6, the'cam drive, together with a simple switch, providesa reliable means for coordinatingmotor operation withthe transducing head positioning.

Referringto Fig. "2,-it is seen that a reproductioncycle involves rotation of the drum 4 in the-direction of the arrow concurrently with lateral motion ofthe' pickup head 5 across the recording-tape in -the direction of the driving shaft 1. Inaddition-to-providing laterabmotion to the'pickup head, applicants arrangementprovidesrotary motion= of-head 6 to bring it intoand out ofengagement withthe magnetic material-:5 carried-on:- thesurfaceof drum 4.

For this purpose, pickup head is carried by a radial member 39 secured to one end of shaft 1 by set screw 40. During rotation of the cam gear 22 in the direction of the arrow M, friction between the face of cam gear 26 and the mating cam or member 21 tends to rotate the drive shaft 1, and hence also the pickup head in an" angular directionybringingthe pickup head downward I against the magnetic material on the surface of the drum. Sufficient pressure is exerted in this manner to maintain the pickup head against the tape in signal transfer relationship without interfering with the drum rotation. Just before the cams have snapped togethenthat iSyJ'IlSt before member '31 is driven to its -extrem'pos'ition to the right, the drive shaft 1 causes contacts 8 and 9 to open, thereby deenergi'zing motor I. Motor I coasts to a stop thereby preventing any further axial movement of the drive shaft.

If-therecording cycle is to be repeated, switch I0 may be closed, therebycompleting the energizing circuit to themotor and causing it to drive cam gear 22. Drive shaft i continues to move axially to the right until the remainder of 360 revolution of the cams 25 and 21 is completed, whereupon-spring 29, now under compression, causesthe cams-to snap together thereby driving-the drive shaft axially towards the -left.--- In addition, thesprings developed torsional forces cause the driveshaft to rotate in a direction opposite to that shown by arrow 44,-thereby withdrawingthe head. 6 from the tape surface. That-is, thetorsional-forces of the spring in its-compressed state-overcome the normal friction forces'existing between the cam faces to cause rotation "of shaft 1 ina direction opposite to that depicted by-arrow-fil l until the cams snap together: Thereupon, these normal friction forces once again are-effective in causing the pickup head-t0 rotate against the drum surface. As mentioned before, thisrotation is-due to friction between the cam surfaces. This simple friction drivealso permits-the pickup head to be rotated out of the way when a tapechange is desired.

By -mounting themagnetic material on the surface of the drum, -messagesmay bereplaced by the simple expedient of unscrewing the-wing nut, removing theold drumand inserting new dr-umcarrying the new message. Also,-the drum loading permitsdifferent tapes tobe applied to the samedrum in a simple and expedient manner. The drum may be provided with a small grooveon its rimslightly wider than the tape, and a radial slot formed in the rim. The tape is made slightly longer than the-circumference of the drum and has sticky material on each end. One end of the tape is-secured to the ill-'- side of the-'drum-.- It -is then passed through a radial .slot in the rim, around the drum inthe groove, back through the slot and secured to the inside of the rim-.- To facilitate replacing thetape,- the drum-may be removed fromthe motor shaft; The-discontinuity in the tape-at the slot in the rim is not objectionable-inplayback provided the width of the slot isnot excessive.

Since occasions may arise when trackingerror is present, provision-must be provided formoving the drum initially--relative to the pickup head. In the arrangement of Fig. 1, this made possible by movement of an adjusting screw M threaded in; spring leaf bracket 42 carried'by housing 15. Lateralmovement of: the adjusting :screw determines the lateral position of the right-hand side of the output shaft 2. The output shaft 2 is driven by means of a helical gear 3 in a direction so that the action of the gears develops a small axial thrust to the right as shown by arrow 83. This thrust action causes the shaft 2 to bear against the edge of the adjusting screw, thereby positioning the drum with respect to the pickup head 8. Where it is more desirable to drive shaft 2 by means other than a helical gear, such as in friction or belt drives, a spring may be used to produce the end thrust developed by helical gear 3.

Modifications of this invention will occur to those skilled in the art, and it is desired to be understood, therefore, that this invention is not to be limited to the particular embodiments disclosed but that the appended claims are meant to cover all of the modifications which are within the spirit and scope of this invention.

What I claim as new and desire to secure by Letter Patent of the United States is:

l. Transducing apparatus comprising a cylindrical drum rotatable about an axis carrying on its surface a message recorded in a helical track, a driven member rotatable about an axis, a drive shaft positioned coaxially with said driven member and free to rotate relative to said driven memher about said last named axis and free to move axially with respect to said driven member, means for driving said driven member and said drum about their respective axes, a transducing head carried by said shaft and free to rotate into engagement with said surface, a helical driving cam carried by said driven member, a mating member fixed to said shaft, and biased into frictional engagement with said cam for driving said shaft axially to cause said head to scan said surface, said frictional engagement creating a torque directed to press said transducer head into engagement with said surface carrying said message -Til Eon normal forward rotation of said driving means.

2. Transducing apparatus comprising a cylindrical drum rotatable about an axis carrying on its surface a message recorded in a helical track, a driven member rotatable about an axis, a drive a shaft positioned coaxially with said driven mem her and free to rotate relative to said driven member about said last named axis and free to move axially with respect to said driven member, means for driving said driven member and said drum about their respective axes, a transducing head carried by said shaft and free to rotate into engagement with said surface, a helical driving cam having a sudden discontinuity carried by said driven member, a mating member fixed to said shaft, and biasing means for biasing said mating member into frictional engagement with said cam for driving said shaft axially to cause said head to scan said surface, said frictional engagement creating a torque directed to press said transducer head into engagement with said surface carrying said message upon normal forward rotation of said driving means, said biasing means comprising a helical spring having one end in engagement with a stationary surface, and the other end engaging said shaft, said helical spring being wound in a direction so that upon said mating member reaching said discontinuity, with said helical spring in a compressed condition, said helical spring imparts a torque to said shaft directed to cause said transducer to lift from said surface.

LEONARD M. BARKER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 653,698 Robb July 17, 1900 672,586 Arnold Apr. 23, 1901 1,185,559 Vaughan May 30, 1916 2,014,495 Goldhammer Sept. 17, 1935 2,087,135 Wielage July 13, 1937 2,166,079 Ricchiardi July 11, 1939 2,168,792 Daniel Aug. 8, 1939 2,229,293 Huntley et a1 Jan. 21, 1941 2,468,198 Heller Apr. 26, 1949 FOREIGN PATENTS N umber Country Date 799,925 France Apr. 20, 1936 

